In 1969, the U.S. Army Corps of Engineers temporarily stopped the water flow over the American Falls at Niagara Falls by building a rock cofferdam upstream. This exposed a dry canyon for the first time in millennia, revealing a huge pile of fallen boulders, scattered coins, lost artifacts, and even two human skeletons. The goal was to study erosion and stabilize the cliff before eventually restoring the water. With the falls dry, engineers documented the bare rock face and the massive talus pile at its base. The exposed riverbed created an eerie and silent scene, a stark contrast to the thunderous waterfall usually seen there. Workers installed anchors, examined the cliff, and considered removing debris, but ultimately decided the boulders were essential for maintaining the falls' shape. After about six months, the cofferdam was detonated in November 1969, allowing water to flow over the falls once again. More historical photos: